Steering system for off-road vehicle

ABSTRACT

An off-road vehicle includes a frame and wheels. An engine powers the wheels through a drive system that includes a front differential gear unit. A housing encloses the front differential gear unit. The housing is positioned generally on a longitudinal center plane of the frame with the plane extending generally vertically and fore to aft. A steering system controls directional movement of the front wheels. The steering system includes a steering wheel that is offset relative to the center plane. A steering shaft is connected to the steering wheel and is disposed on the frame for rotation. A pair of tie-rods are coupled with the respective front wheels. A coupling mechanism couples the steering shaft to the tie-rods. The coupling mechanism converts the rotary movement of the steering shaft to an axial movement of each tie-rod. The coupling mechanism includes a rack-and-pinion assembly. A gear case encloses the rack-and-pinion assembly. The gear case is coupled with the differential housing and positioned such that the center plane intersects the gear case.

PRIORITY INFORMATION

[0001] The present application is based on and claims the benefit ofU.S. Provisional Application No. 60/459,947, filed on Apr. 2, 2003,under 35 U.S.C. § 119.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a steering system foran off-road vehicle, and more particularly to an improved steeringarrangement for an off-road vehicle.

[0004] 2. Description of Related Art

[0005] Off-road vehicles are designed to be operated over ruggedterrain. These vehicles are often operated off-road over terrain suchas, for example, steep inclines and declines, rough roads, and areascovered in mud and water.

[0006] Off-road vehicles typically include a frame that is supported bywheels. In one common arrangement, the vehicle has four wheels, i.e., apair of front wheels and a pair of rear wheels. A prime mover, such asan internal combustion engine, for instance, is employed to power atleast the rear or front wheels, and most commonly, all of the wheels.Typically, the engine is combined with a transmission to form an engineunit. The transmission transfers power to an output shaft from acrankshaft of the engine. The output shaft drives the wheels through adrive line assembly. For example, Japanese Utility Model PublicationJP-Y2-H6-34213 discloses such an arrangement.

SUMMARY OF THE INVENTION

[0007] The off-road vehicle can include a steering system that controlspivotal movement of the front wheels. In one arrangement, the steeringsystem has a steering shaft that is mounted on the frame for rotationalmovement. In some arrangements, the off-road vehicle has seatingpositions laterally disposed relative to each other (e.g., side byside), one for a driver and another for a passenger. In sucharrangements, the steering shaft can be positioned forward of one of theseating positions (e.g., in front of a driver's seat). A lower portionof the shaft is connected to the front wheels with tie rods. In somearrangements, a rack and pinion arrangement can couple the shaft to thetie rods such that axial movement of the tie rods is induced byrotational movement of the shaft. The rack and pinion arrangement caninclude rod ends that extend outward toward the respective tie rods. Aninner ball joint can couple the rod ends to the tie rods. In addition,an outer ball joint can couple the tie rods with a knuckle armassociated with each wheel. Typically, a king pin extends from an axleof the front wheel and is joined to the knuckle arm.

[0008] In some arrangements, the off-road vehicle can be provided with asuspension system that allows each wheel to move independently of theother wheels. In such arrangements, the outer ball joint is able to movearound on an imaginary spherical surface that has the inner ball jointas a center of the sphere. The knuckle arm, however, generally is onlycapable of generally vertical movement along a curve that is regulatedby the geometry of the suspension linkage. The knuckle arm, thus,rotates about the king pin and causes bump steering unless the linkagecurve is very similar to the spherical surfaces defined by the balljoint geometry.

[0009] Bump steering generally can be defined as the instances in whichthe wheels steer themselves without any input from the steering wheel.This undesirable steering generally is caused by bumps in the road andan interaction of improper lengths and/or angles in the suspension andsteering linkages. During bump steering, the toe angle of the wheel alsovaries, typically in an undesirable manner.

[0010] In arrangements featuring an off-center steering shaft (e.g.,steering wheel positioned forward of one of a pair of side-by-sideseating positions), the tie rod on this side is shorter than the tie rodwould be if the steering shaft were centrally positioned on the vehiclein a lateral direction. To compensate for the shortened tie rod, the tierod on the other side also is shortened to maintain a symmetricalconstruction. As a result of the shortened tie rods, the imaginaryspherical surfaces defined on both sides of the vehicle have a smallercircumference than those that would be defined when the steering systemis centrally disposed. With the smaller circumference, the curve definedby the suspension linkage can easy become misaligned with the imaginaryspherical surface, which results in greater occurrences of bumpsteering.

[0011] The wheel suspension can be specially designed to reduce bumpsteering and to decrease the amount of toe angle change duringsuspension travel. Such specially suspension designs, however, arelimited and cause severe constraints in suspension and steering design.

[0012] A need, therefore, exists for an improved steering system for anoff-road vehicle that can reduce bump steering without significantlylimiting the design choices of such systems.

[0013] One aspect of an embodiment of the present invention involves anoff-road vehicle comprising a frame. A first wheel and a second wheelsupport a forward portion of the frame. A generally verticallongitudinal center plane is defined through the frame the first wheelis disposed on one side of the center plane and the second wheel isdisposed on an opposite side of the center plane. A prime mover issupported by the frame. A drive system connects the prime mover to thefirst and second wheels. A housing encloses a portion of the drivesystem. The housing is positioned generally on the center plane of theframe. A steering system is connected to the first and second wheels.The steering system comprises a steering control member. The steeringcontrol member is adapted for use by a driver of the vehicle. Thesteering control member is off-set relative to the center plane. Anupper end of a steering shaft is connected to the steering member. Thesteering shaft defines an axis of rotation. The steering shaft issupported by the frame and is rotatable about the axis of rotation. Afirst tie-rod is connected to the first wheel and a second tie-rod isconnected to the second wheel. A coupling assembly joins the steeringshaft to the first and second tie-rods. The coupling assembly is adaptedto convert rotation of the steering shaft to axial movement of the firstand second tie-rods. A case encloses at least a portion of the couplingassembly and the case is secured to the housing such that the couplingassembly is intersected by the center plane.

[0014] Another aspect of an embodiment of the present invention involvesan off-road vehicle comprising a frame. A first wheel and a second wheelare arranged to support a forward portion of the frame. A generallyvertical center plane extends fore and aft along the frame. The centerplane generally bisects the frame. The center plane is interposedbetween the first wheel and the second wheel. A prime mover ispositioned above a central portion of the frame. A drive system isarranged to transmit power of the prime mover to the first and secondwheels. The drive system comprises a differential gear unit configuredto distribute power to the first and second wheels. A housing has atleast a portion that generally encloses the differential gear unit. Thecenter plane intersects the portion of the housing containing thedifferential gear unit. A steering system is connected with the firstand second wheels. The steering system comprises a steering controlmember. The steering control member is positioned to a lateral side ofthe center plane. A case encloses a portion of the steering system. Thecase is coupled with the housing and is positioned such that the centerplane also intersects at least a portion of the case enclosing theportion of the steering system.

[0015] A further aspect of an embodiment of the present inventioninvolves an off-road vehicle comprising a frame. A first wheel and asecond wheel support a forward portion of the frame. A generallyvertical plane extend fore and aft and are disposed centrally betweenthe first wheel and the second wheel. A prime mover is positioned abovea portion of the frame. A drive system transmits power to the first andsecond wheels from the prime mover. A housing encloses a portion of thedrive system. The housing is intersected by the center plane of theframe. A steering system is connected to the first and second wheels.The steering system comprises a steering control member that is adaptedfor direct control by a driver of the vehicle. The steering controlmember is positioned substantially to one side of the center plane. Acase encloses a portion of the steering system that is intersected bythe center plane. The portion of the steering system that is intersectedby the center plane transforms movement of the steering control memberinto movement of the front wheels. The case is coupled with the housingthat encloses the portion of the drive system.

[0016] Another aspect of an embodiment of the present invention involvesan off-road vehicle comprising a frame. A first wheel and a second wheelare independently suspended from the frame. The first and second wheelsare steerable relative to the frame. A prime mover is supported by theframe. A drive shaft transfers power from the prime mover. Adifferential gear unit receives power from the drive shaft. Thedifferential gear unit supplies power to the first and second wheels. Agenerally vertical center plane extends in a longitudinal direction andis positioned generally equidistant between the first and second wheels.An operator control member is mounted to the frame assembly and isrotatable about a first axis. The operator control member is positionedsubstantially on one side of the center plane. A steering mechanism isadapted to transform rotation of the control member about the first axisinto generally linear lateral movement of a first rod section and asecond rod section. The first rod section is coupled with a first tierod. The first tie rod is coupled with the first wheel. The second rodsection is coupled with a second tie rod. The second tie rod is coupledwith the second wheel. The steering mechanism is positioned such that itis intersected by the center plane and is joined to a casing covering atleast a portion of the differential gear unit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other features, aspects and advantages of thepresent invention are described in detail below with reference to thedrawings of a preferred embodiment, which is intended to illustrate andnot to limit the invention. The drawings comprise six figures in which:

[0018]FIG. 1 is a side elevational view of an off-road vehicleconfigured in accordance with a preferred embodiment of the presentinvention;

[0019]FIG. 2 is a top plan view of the off-road vehicle of FIG. 1;

[0020]FIG. 3 is a side elevational view of an engine unit of theoff-road vehicle;

[0021]FIG. 4 is a side elevational view of a front differential and aportion of a steering system of the off-road vehicle;

[0022]FIG. 5 is a partial sectional view taken along the line 5—5 ofFIG. 2; and

[0023]FIG. 6 is a partial sectional view taken along the line 6—6 ofFIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] With reference to FIGS. 1-7, an off-road vehicle is described.While the embodiment of the present invention is described in connectionwith this particular type of vehicle, those of skill in the art willappreciate that certain features, aspects, and advantages of the presentinvention may have utility in a wide range of applications for othervehicles. For instance, certain features, aspects and advantages of thepresent invention can be used with snow vehicles, tractors, utilityvehicles, and the like.

[0025] With reference to FIGS. 1, 2 and 5, the off-road vehicle 30preferably has an open tubular-type frame 32. The illustrated frame 32comprises a main frame section 34, a front frame section 36, a rearframe section 38 and a compartment frame section (or pillar framesection) 40.

[0026] The main frame section 34 includes a pair of side frame units 42spaced apart side by side with each other. Each side frame unit 42comprises a front tubular member 42 a and a rear tubular member 42 b.Each tubular member 42 a, 42 b preferably is rectangular in section butother configurations can be used. In one variation, the front and rearmembers 42 a, 42 b can have a circular shape in section. Moreover, themembers 42 a, 42 b can have an incomplete tubular shape such as, forexample, a U-shape. A rear end of the front tubular member 42 a is bentoutwardly and is coupled with a mid portion of the rear tubular member42 b. A forward end of the rear tubular member 42 b is bent inwardly andis coupled with a mid portion of the front tubular member 42 a. Thus, inthe illustrated arrangement, both of the front and rear tubular members42 a, 42 b are nested together. The side frame units 42 preferably areconnected by front, center and rear cross members 44 (FIG. 2) thattransversely extend between the tubular members 42 a, 42 b.

[0027] The front frame section 36 extends generally upward from a frontportion of the main frame section 34. The rear frame section 38 alsoextends generally upward from a rear portion of the main frame section34. The rear frame section 38 preferably includes a pair of rear framemembers 46. Several struts connect the rear frame members 46 to the sidemembers 42 of the main frame section 34 and support the rear framemembers 46 above the side members 42.

[0028] The compartment frame section 40 is disposed generally betweenthe front and rear frame sections 36, 38 in a side view as shown inFIG. 1. The compartment frame section 40 includes a pair of compartmentmembers 48 extending generally upward and higher than the front and rearframe sections 36, 38. The compartment members 48 are spaced apart fromeach other on both sides of the off-road vehicle 30 to be placed moreoutward than the main frame section 34 in the illustrated embodiment.

[0029] A floorboard or floor panel 50 extends in an area generallydefined by the compartment members 48 in the top plan view (FIG. 2) andis affixed at least to the main frame 34. The floorboard 50 defines apassenger compartment together with the compartment frame section 40. Asbest shown in FIG. 5, the illustrated floorboard 50 generally is a flatpanel with a portion that projects upward. That is, the floorboard 50comprises a horizontal section 51 defining a generally flat area and aprojection 52 defining a tunnel extending along a longitudinal centerplane LC (FIG. 2) of the frame 32 that extends vertically and fore toaft. The horizontal section 51 can support feet of a driver and apassenger and also can be used as a step when the driver or thepassenger enters or leaves the passenger area of the off-road vehicle30. The illustrated projection 52 is configured as a trapezoid insection and thus has slanted side surfaces 53 and a top surface 54.Other configurations also can be used.

[0030] The main, front, rear and compartment frame sections 34, 36, 38,40 preferably are welded to each other. The illustrated structure andarrangement of the frame 32, and the combination of the frame 32 and thefloorboard 50 are merely one example. Various structures, arrangementsand combinations other than those are practicable. For instance, therespective frame sections 34, 36, 38, 40 can be provided with struts orreinforcement members that are not described above.

[0031] With reference to FIGS. 1 and 2, the off-road vehicle 30preferably has a pair of front wheels 56 and a pair of rear wheels 58both supporting the frame 32. Each wheel 56, 58 preferably has a tirethat is sized and configured to advantageously proceed over rough roadsand in mud and water. Relative to most similar conventional off-roadvehicles, the tire can have a higher internal pressure and/or can beequipped with an inner tube, if desired. In some embodiments, a tubelesstire, which is relatively wide and which has a relatively low airpressure, can be used. In one arrangement, the selected tires are sizedas follows: 25×8-12 at the front end and 25×10-12 at the rear end.

[0032] The front and rear wheels 56, 58 preferably are coupled with theframe 32 through a front suspension mechanism 60 and a rear suspensionmechanism 62, respectively. The front suspension mechanism 60 swingably(up and down) and independently suspends both the front wheels 56. Therear suspension mechanism 62 also swingably (up and down) andindependently suspends both the rear wheels 58. Thus, the illustratedoff-road vehicle 30 preferably features four wheel independentsuspension.

[0033] With reference to FIGS. 1-3, the off-road vehicle 30 preferablyhas a seat unit 66. The illustrated seat unit 66 comprises a pair ofseats or seat sections 68 such that the driver and the passenger can sitside by side. In some arrangements, the seat unit 66 can comprise abench style, or split bench style, seat. In such arrangements, two ormore seating positions are positioned laterally across the vehicle.

[0034] In the illustrated arrangements, a pair of separate seat sections68 are provided. The rear frame section 38, at least in part, forms apair of seat pedestals (not shown). Each seat 68 and each seat pedestaltogether form a seat assembly. The illustrated off-road vehicle 30 thushas two sets of seat assemblies. The seat assemblies are spaced apartfrom each other to form a space 70 (FIG. 2) therebetween.

[0035] A preferable construction or structure of an off-road vehiclesimilar to the off-road vehicle 30 is disclosed in, for example, aco-pending U.S. application filed on , titled “ENGINE ARRANGEMENT FOROFF-ROAD VEHICLE,” having attorney docket number FY.51034US1A, aco-pending U.S. application filed on, titled “OFF-ROAD VEHICLE WITHTRANSMISSION,” having attorney docket number FY.51035US1A, a co-pendingU.S. application filed on, titled “AIR INTAKE SYSTEM FOR OFF-ROADVEHICLE,” having attorney docket number FY.51036US1A, a co-pending U.S.application filed on, titled “FLOOR ARRANGEMENT FOR OFF-ROAD VEHICLE,”having attorney docket number FY.51037US1A, a co-pending U.S.application filed on, titled “OFF-ROAD VEHICLE WITH AIR INTAKE SYSTEM,”having attorney docket number FY.51039US1A, a co-pending U.S.application filed on, titled “OFF-ROAD VEHICLE WITH WHEEL SUSPENSION,”having attorney docket number FY.51040US1A, a co-pending U.S.application filed on, titled “FRAME ARRANGEMENT FOR OFF-ROAD VEHICLE,”having attorney docket number FY.51042US1A, and a co-pending U.S.application filed on, titled “TRANSMISSION FOR OFF-ROAD VEHICLE,” havingattorney docket number FY.51043US1A, the entire contents of which arehereby expressly incorporated by reference.

[0036] In this description, the terms “front” and “forward” mean thedirection in which the driver or passenger looks straight when seated onthe seats 68. Also, the terms “rear,” “rearward” and “backward” mean thedirection opposite to the front direction.

[0037] Each seat 68 preferably comprises a seat cushion 72 and a seatback 74. The seat cushion 72 extends generally horizontally over theseat pedestal and is detachably or removably affixed to the seatpedestal. The seat back 74 extends generally vertically and upward froma rear portion of the seat cushion 72. In the illustrated arrangement,the seat cushion 72 and the seat back 74 are formed unitarily. In onevariation, the seat cushion 72 and the seat back 74 can be separatelyformed and assembled together.

[0038] With reference to FIG. 3, the illustrated seat unit 66 has aforward end 78, a rear end 80 and a top end 82. In this arrangement, theforward end 78 of the seat unit 66 is defined by forward ends of theseat cushions 72. If, however, the seat pedestals extend forward of theseat cushions 72, forward ends of the seat pedestals can define theforward end of the seat unit 66. An imaginary forward, generallyvertical plane 84 can be defined through the forward end of the seatunit 68.

[0039] The rear end 80 and the top end 82 preferably are defined by rearends of the seat backs 74 and top ends of the seat backs 74,respectively. An imaginary rearward, generally vertical plane 86 can bedefined through the rear ends of the seat backs 74. Also, an imaginary,generally horizontal plane 88 can be defined through the top ends 82 ofthe seat backs 74. The seat 68, however, can be shaped in variousconfigurations. The seat back may be omitted under some circumstances.If the seat back 74 is omitted, the imaginary rear, generally verticalplane 86 can be defined more forwardly as indicated by the referencenumeral 86A. Furthermore, the rear, generally vertical plane 86 may bedefined more forwardly as indicated by the reference numeral 86B if thethickness of the seat back 74 is reduced. Also, the generally horizontalplane 88 may be shifted downward to a top surface 82A of each of theseat cushions 72 as indicated by the reference numeral 88A.

[0040] Thus, the forward, rear and top ends 78, 86, 82, the imaginaryforward and rear generally vertical planes 84, 86 and the imaginarygenerally horizontal plane 88 are normally determined depending on aconfiguration of the seat assembly, which includes the seat 68 and theseat pedestal in the illustrated arrangement. More practically, the rearend 86 should be substantially on the imaginary, generally verticalforward plane 86A or the imaginary, generally vertical rear plane 86B.Also, the top end 82 should be substantially the top surface 82A of theseat cushions 72 and should be on the imaginary, generally horizontalplane 88A.

[0041] Because the seats 68 are positioned on the seat pedestals, whichhave a certain height, a relatively large space is formed below theimaginary horizontal plane 88A. Additionally, the seat unit 66 can haveany number of seats, such as, for example, three seats in somealternative arrangements.

[0042] With reference to FIGS. 1, 2 and 6, the off-road vehicle 30preferably has a carrier or cargo box 92 behind the seat unit 66. Theillustrated carrier 92 extends over a rear portion of the rear framesection 38 and is suitably affixed at least to the rear frame members46. In one arrangement, the carrier 92 can be tipped rearward to allowits contents to be dumped. The carrier 92 preferably is formed generallyin the shape of a rectangular parallelepiped and has a bottom, a front,a rear and a pair of lateral sides. That is, the carrier 92 is generallyconfigured as an open-topped box.

[0043] As best shown in FIG. 6, the bottom of the carrier 92 preferablycomprises steps 96 on both sides such that side portions 98 of thebottom are positioned higher than a central portion 100 of the bottom.The steps 96 advantageously reduce the likelihood that the rear wheels58 would contact carrier 92 when the rear wheels 58 are in an upper mostposition of suspension travel. It should be noted that the describedmovement of the rear wheels 58 is the relative movement thereof inrelation to the carrier 92. The center bottom portion 100 thus increasesthe capacity of the carrier 92. Each step 96 preferably extends fore toaft as shown in FIG. 2. Longitudinally shortened steps (similar to wheelwells) also can be used.

[0044] The center bottom portion 100 helps lower the center of gravityof the carrier 92. The illustrated off-road vehicle 30 thus featuresenhanced stability. The steps 96 also reduce lateral movement of loads.Manufacture of the carrier 92 is simple and cost effective because thesteps 96 only extend fore to aft. In addition, the steps 96 may increasethe stiffness of the carrier 92.

[0045] With reference to FIGS. 1, 2 and 4, the off-road vehicle 30comprises a steering mechanism 104. The steering mechanism 104 in theillustrated arrangement includes a steering wheel 106. The steeringwheel 106 is affixed to the frame 32 for steering movement in front ofthe seat 68 for the driver, which is located on the left-hand side ofthe illustrated off-road vehicle 30.

[0046] The illustrated steering mechanism 104 preferably comprises asteering shaft unit 110 coupled with the steering wheel 106, a tie-rod(not shown) coupled with the front wheels 56, and a rack-and-pinionassembly 112 (FIG. 4) that connects the steering shaft unit 110 to thetie-rod. The rack-and-pinion assembly 112 converts the pivotal movementof the steering wheel 106 to an axial movement of the tie-rod. Therack-and pinion assembly 112 preferably is housed in a gear case 114.

[0047] The steering wheel 106 can be rotated clockwise andcounterclockwise to effect turning movement of the steerable wheels. Insome arrangements, a control stick can be used in place of a steeringwheel 106. Other suitable directional control devices also can be used,such as, without limitation, handlebars, push-buttons, foot pedals andthe like.

[0048] As best shown in FIG. 2, the illustrated steering shaft unit 110comprises an upper steering shaft 116 and a lower steering shaft 118both pivotally affixed to the frame 32. The upper shaft 116 extendsupward and rearward toward the driver's area and the steering wheel 106is affixed to the top end of the upper shaft 116. The upper shaft 116preferably extends generally parallel to the longitudinal center planeLC. The lower shaft 118 extends toward the longitudinal center plane LC(i.e., toward a laterally central area of the vehicle) from a lower endof the upper shaft 116 through a universal joint (not shown) and iscoupled with the rack-and-pinion assembly 112, which is mounted withinthe case 114.

[0049] The tie rods preferably are connected to rod sections that extendoutward from the rack and pinion assembly 112. In some arrangements, aninner ball joint couples the rod sections to the respective tie rods.Also, an outer ball joint preferably couples each tie rod to a knucklearm (not shown) that is associated with each front wheel 56. Eachknuckle arm is coupled with a king pin (not shown) that extends from anaxle of the front wheel 56. The tie-rods move axially along with the rodsections when the steering shaft 110 is rotated.

[0050] As described above, the vehicle 30 preferably includes four wheelindependent suspension. In such arrangements, as discussed above, theouter ball joints can move around on an imaginary sphere that is definedabout the inner ball joint. In other words, the outer ball joint canmove transversely as well as around the surface of the imaginary sphere.The knuckle are is only capable of moving along an arc defined by thesuspension link connecting the wheel to the frame. The knuckle arm,thus, rotates about the king pin and causes bump steering unless thecurve defined by the suspension link is consistent with the spheredefined about the inner ball joint. In addition, bump steering causeschanges in the toe angle of the front wheels.

[0051] To reduce bump steering, as shown in FIG. 4, the gear case 114preferably is mounted on a front differential housing 122. The frontdifferential housing 122 advantageously is positioned on thelongitudinal center plane LC of the frame 32. The front differentialhousing 122 also preferably is disposed between the front tubularmembers 42 a at a location just rearward of a forwardmost cross member44 in the illustrated arrangement. In one arrangement, the gear case 114can be unitarily formed with the differential housing 122. The frontdifferential housing 122 incorporates a front differential gear unit 124and is relatively stiff. The gear case 114 preferably has a bracket 126extending downward and the differential housing 122 comprises a mountsurface 128. The bracket 126 is affixed to the mount surface 128 bybolts 130 or other suitable mounting techniques.

[0052] Preferably, the mount surface 128 is a top surface of the housing122. That is, a bottom surface of the illustrated gear case 114 can besecured to the top surface of the housing 122. Accordingly, sufficientclearance can be provided adjacent another surface of the gear case 114to enable the lower steering shaft 118 to be coupled to therack-and-pinion assembly 112. The illustrated arrangement alsoadvantageously enables the steering shaft 110 to be shortened, whichdecreases its weight, because the surface adjacent to the couplingregion is closer to the top surface 128 of the housing 122. Moreover,the tie-rods are positioned in the illustrated arrangement in a mannerthat reduces the likelihood that they will interfere with the shafts ofthe front differential 124, which are described in greater detail below.

[0053] Because the front differential housing 122 and the gear case 114are secured together at a location along the longitudinal center planeLC, the tie-rods can be elongated relative to a construction in whichthe gear case 114 is mounted off-center with respect to the longitudinalcenter plane LO. Further, the tie-rods can have substantially equallengths to each other while also being elongated in the illustratedarrangement. The elongation of the tie rods results in an increaseddiameter or circumference of the imaginary spherical surface. Theenlarged imaginary spherical surface greatly increases the availablesuspension designs with which bump steering can be reduced. Moreover,the illustrated arrangement greatly decreases the toe angle changes ofthe right and left front wheels 56 caused by movements controlled by thesuspension system. Accordingly, greater design freedom is provided whilesimultaneously reducing bump steering. Furthermore, no special bracketsor stays are used to mount the rack and pinion arrangement (e.g., thegear case 114) and the gear case 114 can be securely mounted to theframe 32 through the front differential housing 122. During assembly ofthe vehicle, the gear case 114 can be affixed to the front differentialhousing 122 before the housing 122 is affixed to the frame 32 whicheases assembly because the connection of the front differential housing122 and the gear case 144 can occur outside of the cramped space withinthe vehicle.

[0054] Also, the mounting arrangement only requires the mount surface128 to be formed on the differential housing 122, because the gear case114 can have the bracket 126 regardless whether the gear case 114 isaffixed to the differential housing 122 or not.

[0055] With reference to FIGS. 1 and 2, a hood or bonnet 134 surroundsat least a front portion of the main frame section 34, the front framesection 36, the front wheels 56 and a major portion of the steeringmechanism 104. A dashboard 136 preferably depends from a rear portion ofthe hood 134. The dashboard 136 faces toward the passenger compartmentand a meter unit 138 preferably is disposed in a central portion of thedashboard 136. The meter unit 138 preferably incorporates meters and/orgauges such as, for example, a speedometer, a fuel level meter, and thelike. Because of this meter unit arrangement, the driver can easily viewthe individual meters at a glance.

[0056] With reference to FIGS. 1-5, the off-road vehicle 30 has a primemover that powers the off-road vehicle 30 and particularly the front andrear wheels 56, 58. The prime mover preferably is an internal combustionengine 142. Alternatively, an electric motor can replace the engine 142.Engine power is transferred to the front and rear wheels 56, 58 througha suitable transmission 144 and a suitable drive mechanism 146. In theillustrated arrangement, the engine 142 and the transmission 144 arecoupled together to form an engine unit 148. The illustratedtransmission 144 advantageously includes an endless V-belt transmissionmechanism and a switchover mechanism. The illustrated drive mechanism146 comprises a forward driveshaft 150 extending forward from the engineunit 148, a rear driveshaft 152 extending rearward from the engine unit148, the front differential 124 is coupled with the front axles (notshown) of the front wheels 56, and a rear differential 154 is coupledwith the rear axles (not shown) of the rear wheels 58. In somearrangements, a single axle can replace the half axles.

[0057] As shown in FIGS. 1-3, the engine unit 148 preferably ispositioned generally lower than the imaginary, generally horizontalplane 88 and generally in the space 70 defined between the seatassemblies. The illustrated engine 142 operates on a four-strokecombustion principle, however, other engine operating principles alsocan be used. The engine 142 preferably has a single cylinder block 158that extends generally upward and rearward from a lower section of theengine unit 148. That is, the cylinder block 158 has a cylinder axis CAthat inclines relative to vertical at a certain angle. The illustratedcylinder axis CA inclines from vertical at approximately 45 degrees.

[0058] In the illustrated arrangement, the engine 142 is an internalcombustion engine. As such, the cylinder block 158 preferably defines acylinder bore (not shown) therein. A piston (not shown) is reciprocallydisposed within the cylinder bore (not shown). A cylinder head 160preferably closes an upper end of the cylinder bore to define, togetherwith the cylinder bore and the piston, a combustion chamber 163.

[0059] The cylinder head 160 also defines a pair of intake ports 162 anda pair of exhaust ports 166 that communicate with the combustion chamber163. An intake valve can be provided at each intake port 162 toselectively open the combustion chamber 163 to an air intake system 164.In the illustrated arrangement, the air intake system 164 is coupledwith the intake ports 162 at a front surface 165 of the cylinder head160. The front surface 165 of the cylinder head 160 preferably isdisposed substantially within the space 70 and preferably facesgenerally forward and upward. With reference to FIG. 2, the frontsurface 165 desirably is disposed generally between the seats 68.

[0060] The air intake system 164 introduces air into the combustionchamber 163 through the intake ports 162 when the intake valves (notshown) open the passage into the combustion chamber 163. An exhaustvalve (not shown) also is provided at each exhaust port 166 toselectively open the combustion chamber 163 to an exhaust system 168. Inthe illustrated arrangement, the exhaust system 168 is coupled with theexhaust ports 166 at a rear surface 169 of the cylinder head 160. Therear surface 169 of the cylinder head 160 is positioned substantiallyopposite to the front surface 165 and generally faces rearward anddownward. The exhaust system 168 routes exhaust gases from thecombustion chamber 163 to an outside location.

[0061] A cylinder head cover 170 is attached to the cylinder head 160 toenclose one or more camshafts (not shown). The camshafts (not shown)preferably are journaled on the cylinder head 160. The camshafts (notshown) actuate the intake and exhaust valves at speeds that aregenerally in proportion to the engine speed. Other suitable methods ofactuating the valves also can be used.

[0062] An upper section of the illustrated engine unit 148 includes thecylinder block 158, the cylinder head 160 and the cylinder head cover170. The upper section at least in part extends rearwardly beyond theimaginary rear, generally vertical plane 86 (and 86A or 86B).

[0063] A lower section of the engine unit 148, which is the balance ofthe engine unit 148, comprises a crankcase 174, which closes a lower endof the cylinder bore (not shown). A crankshaft 176 preferably isjournaled within the crankcase 174 and is coupled with the piston (notshown) in any suitable manner. In the illustrated arrangement, thecrankshaft 176 extends generally transverse to a direction of travel ofthe vehicle but other orientations also can be used. The reciprocalmovement of the piston results in rotation of the crankshaft 176. Thecrankshaft 176 preferably drives the camshafts via a camshaft drivemechanism.

[0064] The crankcase 174 also houses an input shaft for a shiftableportion of the transmission 144. The input shaft is positioned forwardof the crankshaft 176. The lower section of the engine unit 148 alsocomprises a V-belt housing 178, which is positioned next to thecrankcase 174 in the illustrated arrangement. Moreover, in theillustrated arrangement, the V-belt housing 178 is defined on theleft-hand side of the crankcase 174. The V-belt housing 178 houses theV-belt transmission mechanism (e.g., continuously variabletransmission). Thus, the lower section of the engine unit 148 (whichcomprises at least the crankcase 174 and the V-belt housing 178) alsodefines, at least in part, a transmission housing 180. The transmission144 will be described in greater detail below.

[0065] With reference to FIGS. 1-3 and 5, the illustrated air intakesystem 164 extends forward to a location under the hood 134 from theintake ports 162 of the engine 142. The intake system 164 preferablycomprises a throttle body or carburetor 182, an accumulator or plenumchamber 184, an air intake duct 186 and an air cleaner unit 188.

[0066] With reference to FIG. 3, the throttle body 182 is connected tothe intake ports 162 through an air intake conduit 192. The throttlebody 182 comprises a throttle valve 194 that regulates a rate of airflowamount delivered to the combustion chamber 163. The throttle valve 194preferably is a butterfly valve and generally is journaled for pivotalmovement. The level of airflow depends on an angular position of thethrottle valve 194—when the throttle valve is closed or substantiallyclosed, minimal air flow results, while when the throttle valve isopened or substantially opened, maximum air flow results.

[0067] An accelerator pedal or control member 196 (FIG. 5) preferably isdisposed at a front end of the floorboard 50 for pivotal movement tocontrol the position of the throttle valve 194. A throttle cableconnects the accelerator pedal 196 to the throttle valve 194. The driverthus can control the throttle valve 194 by adjusting an angular positionof the accelerator pedal 196 with a foot 198. Normally, the greater thethrottle valve 194 opens, the higher the rate of airflow amount and thehigher the engine speed. Other suitable mechanisms and/or electricalconnections also can be used to transmit operator demand to the throttlevalve or engine.

[0068] With reference to FIG. 5, the heel (i.e., lower portion of thefoot 198) of the driver can lean against the slanted side surface 53 onthe left-hand side of the projection 52 when the foot 198 is in positionto operate the accelerator pedal 196 because the slanted side surface 53is located generally adjacent to the accelerator pedal 196. In otherwords, the slanted portion 53 functions as a foot brace and reduces thelikelihood that the operator's foot 198 will slide off of theaccelerator pedal 196 when the off-road vehicle 30 is operated overrough terrain or when the off-road vehicle 30 turns a sharp comer at arelatively high speed, which increases the centrifugal forcestransmitted to the foot 198. Thus, the illustrated construction canprovide the driver with better body control and improved driving bodyposition. Similarly, the slanted side surface 53 on the right-hand sidealso can function as the foot brace. Thus, the passenger, or driver insome configurations, can also have a foot brace for use during operationof the vehicle.

[0069] With reference again to FIG. 3, the throttle body (e.g., thecarburetor) 182, which functions as a charge former, preferably also hasa fuel measurement mechanism that measures an amount of fuel mixed withthe air in accordance with the rate of airflow. Because of this fuelmeasurement mechanism, the air/fuel ratio supplied to the engine can becontrolled and/or optimized depending upon engine operating conditions.The fuel is delivered to the throttle body 182 from a fuel tank (notshown) that can be suitably mounted and suitably positioned on the frame32.

[0070] Other charge formers such as, for example, a fuel injectionsystem can be used. The fuel injection system has a fuel injector thatis configured to spray fuel directly into the combustion chamber 163 orinto a portion of the air intake system downstream of the throttlevalve. An engine control unit (ECU) can control the amount of fuelinjected, for example, in accordance with the airflow rate.

[0071] With reference to FIGS. 1 and 2, the accumulator 184 can becoupled with an inlet of the throttle body 182. The accumulator 184generally forms a portion of the intake duct 186 in the broad sense ofthe term but provides a larger volume or cross-sectional area ascompared to the balance of the intake duct 186. Such a constructionallows air to accumulate prior to delivery to the throttle body 182. Asbest shown in FIG. 1, the accumulator 184 is generally shaped as anarcuate configuration. Such a construction advantageously smoothens thedelivery of air to the engine. Furthermore, because the accumulator 184has a relatively large volume and is disposed next to the throttle body182, the intake efficiency of the induction system is greatly improved.That is, sufficient air can be quickly supplied to the engine 142 evenwhen the engine is being operated at a relatively high engine speed.This is advantageous due to the longer length of the intake duct 186.

[0072] In the illustrated arrangement, the air intake conduit 192, thethrottle body 182 and the accumulator 184 together extend forwardly ofthe engine within a region defined between the seats 68. Upper portionsof the throttle body 182 and the accumulator 184 preferably arepositioned slightly higher than the top ends 82A of the seat cushions72. A forward-most portion of the accumulator 184 turns downward at orjust forward of the forward end of the seat assemblies.

[0073] Because of this arrangement, the throttle body 182 and at least aportion of the accumulator 184 are interposed between the seatassemblies and are positioned within, or just adjacent to, the space 70.Thus, the throttle body 182 and the accumulator 184 are positionedwithin a protective region of the vehicle that is located higher than alowermost surface of the frame assembly or the floorboard 50. Suchpositioning reduces the likelihood that dirt and other road debris thatmay be kicked up underneath the vehicle will damage the throttle body182 or the accumulator 184. Such placement also facilitates servicing ofthese components and protects these components from water damage whilefording a stream, a mud bog or the like.

[0074] The illustrated accumulator 184, which is positioned within themost downstream portion of the illustrated intake duct 186, ends above alowermost surface defined by the rear frame section 38. The balance ofthe air intake duct 186, which has a smaller volume or cross-sectionalarea than the accumulator 184, preferably comprises a downstream section200, a middle section 202 and an upstream section 204, which are providea contiguous air flow path in the illustrated embodiment. The downstreamsection 200 extends downwardly from the accumulator 184 to a lowermostportion of the rear frame section 38. The middle section 202 extendsforwardly in a generally horizontal direction from a lower end of thedownstream section 200.

[0075] With reference to FIG. 5, in the illustrated arrangement, themiddle section 202 extends through a tunnel defined by the projection 52of the floorboard 50. Because of this arrangement, the middle section202 advantageously is positioned higher than the horizontal section 51of the floorboard 50, which greatly reduces the likelihood of damagefrom rocks, sticks, road debris or the like. Furthermore, the driverand/or the passenger are able to maintain a good riding body positionbecause the horizontal section 51 is positioned generally verticallylower than the middle section 202. Moreover, the illustrated arrangementcontributes to a lower center of gravity for the off-road vehicle 30because the height of the seats 68 does not need to be increased toaccommodate the middle section 202 or another portion of the airinduction system.

[0076] The middle section 202 preferably ends at a location close to thefront frame section 36. The upstream section 204 extends generallyvertically upward from the middle section 202. In addition, the upstreamsection 204 preferably is positioned within a space defined below thehood 134. To increase the protection from ingestion of water, theforward-most portion of the upstream section 204 extends forward andslightly downward along a lower surface of the hood 134.

[0077] The air cleaner unit 188 preferably is attached at an upstreamend of the intake duct 186 and extends generally along the lower surfaceof the hood 134. The illustrated air cleaner unit 188 has a relativelylarge volume and has a cleaner element therein. The air cleaner unit 188also has an air inlet port. Ambient air is drawn into the air cleanerunit 188 through the air inlet port and passes through the filtrationelement such that foreign substances such as, for example, dust, mud orwater can be substantially removed from the air that is being introducedinto the engine.

[0078] The air, which has been cleaned in the cleaner unit 188, flows tothe accumulator 184 through the intake duct 186. The airflow amount isregulated by the throttle valve 194 in the throttle body 182.Simultaneously, an amount of fuel is measured by the fuel amountmeasurement mechanism in the throttle body 182 in response to the airamount. An air/fuel charge that has a proper air/fuel ratio is formedand is delivered to the combustion chamber 163 when the intake valvesopen the intake ports 162. The air/fuel charge is ignited by an ignitionsystem (not shown) and bums within the combustion chamber 163. Theburning of the charge causes expansion of the gases and increasedpressure that results in movement of the piston. The crankshaft 176 isrotated within the crankcase 174 by the movement of the piston.

[0079] With reference to FIGS. 1-3, the burnt charge, i.e., exhaustgases, are discharged through the exhaust system 168. The illustratedexhaust system 168 preferably comprises a pair of exhaust conduits 208and a muffler 210. The exhaust conduits 208 are coupled with therespective exhaust ports 166 and extend generally rearward. The exhaustconduits 208 extend generally parallel to each other. Preferably, theexhaust conduits 208 have a wavy shape that serpentines up and down, asshown in FIGS. 1 and 2. Rearward ends of the exhaust conduits 208preferably extend beyond a rear end of the rear frame section 38. Themuffler 210 is coupled with the rear ends of the exhaust conduits 208.

[0080] The muffler 210 preferably has a cylindrical shape. A center axisof the muffler 210 preferably extends in a generally transversedirection relative to the longitudinal center plane LC of the frame 32.The muffler 210 has a relatively large volume to reduce exhaust energyand noise. An outlet port 212 can be formed at a side surface, which ison a left-hand side in the illustrated embodiment. Other arrangementsalso can be used. The exhaust gases flow through the exhaust conduits208 and are discharged through the outlet port 212 of the muffler 210.

[0081] The engine 142 can have systems, devices, components and membersother than those described above. For example, the illustrated engine142 can employ a liquid cooling system that uses coolant (e.g., water),which is circulated through a heat exchanger, to cool the engine 142.

[0082] With reference to FIGS. 1-3, the change speed mechanism and theV-belt transmission mechanism together have a common output shaft 216.The output shaft 216 extends generally parallel to the crankshaft 176 ata location in front of the crankshaft 176. The output shaft 216preferably extends through the crankcase 174 and the V-belt housing 178and is journaled for rotation relative to these components. Because ofthis arrangement, the output shaft 216 is positioned at a locationgenerally between the front wheels 56 and the crankshaft 176. In otherwords, the crankshaft 176 is positioned between the output shaft 216 andthe rear wheels 58.

[0083] The crankshaft 176 extends into the V-belt housing 178 andcarries a drive pulley 218 (FIG. 3). The output shaft 216 carries adriven pulley 220. The drive and driven pulleys 218, 220 both comprisean axially fixed pulley member and an axially movable pulley member thatis movable along the respective axis of the crankshaft 176 or the outputshaft 216. Together, the pulley members form a V-shaped valley thatexpands and contracts with changes in engine speed.

[0084] An endless belt 222 or chain, which belt has a V-configuration insection, is wound around the drive pulley 218 and the driven pulley 220.Normally, the movable pulley member of the drive pulley 218 is urged tostay apart from the fixed pulley member by the bias force of a biasmember such as, for example, a spring. The movable pulley member of thedriven pulley 220 is urged to stay close to the fixed pulley member bythe bias force of a bias member such as, for example, a spring.

[0085] Each movable pulley member can move axially against the biasforce by a clutch mechanism which is provided on either pulley 218, 220.The clutch mechanism acts by centrifugal force created when thecrankshaft or output shaft turns at a speed higher than a preset speed.The change in diameter of one pulley causes a corresponding change inthe other pulley. Thus, both diameters of the drive pulley 218 and thedriven pulley 220 vary to automatically change the transmission ratiobetween the drive pulley 218 and the driven pulley 220, normally inresponse to the engine speed.

[0086] With reference to FIGS. 1-3, the V-belt housing 178 preferablyhas an air inlet port 226 at a rear end and an air outlet port 228 at afront end. An air inlet duct 230 (FIGS. 1 and 2) preferably is coupledto the inlet port 226, while an air outlet duct 232 preferably iscoupled to the outlet port 228. The inlet duct 230 extends generallyrearward and upward and generally behind the seat back 74 on theleft-hand side. The inlet duct 230 has an inlet opening 233 that opensforward and is positioned higher than top surfaces of the seat cushions72. The outlet duct 232 extends generally upward and rearward andgenerally along a bottom surface of the seat cushion 72 on the left-handside. The outlet duct 232 has an outlet opening 234 that opens generallyrearward.

[0087] Cooling air is introduced into the V-belt housing 178 through theinlet duct 230 and the air inlet port 226 when the crankshaft 176, theoutput shaft 216 and the drive and driven pulleys 218, 220 rotate. Insome arrangements, one or both of the pulleys can be provided with fanblades to help induce higher speed air flow as the engine speedincreases. Other embodiments can provide a ram air type of air flow.Having circulated with the belt chamber of the transmission, the airthen is discharged through the outlet port 228 and the outlet duct 232.

[0088] With reference to FIGS. 1-3, the engine output that has beentransferred to the output shaft 216 through the V-belt mechanism istransferred to the drive mechanism 146 through the change speedtransmission mechanism. This mechanism preferably is configured toprovide a parking state, a high speed forward state, a neutral state, alow speed forward state, and a reverse state. The mechanism preferablycomprises a suitable gear train that allows an operator to select amongat least the above-mentioned operating states. A bevel gear assembly 236can be coupled with the mechanism.

[0089] The mechanism also comprises a shift lever unit 240 that extendsfrom the crankcase 174. The shift lever unit 240 preferably is connectedto the rest of the switchover mechanism within the crankcase 174 througha suitable linkage (not shown). The shift lever unit 240 preferably isplaced generally within the space defined between the seats 68. Theillustrated lever unit 240 is positioned generally at the forward-mostportion of the space. Such placement facilitates ease of use.

[0090] The shift lever unit 240 preferably comprises a lever 244 and alever cover 246. The lever 244 preferably is affixed to the frame 32directly or indirectly for pivotal movement around a fulcrum. In onevariation, the shift lever unit 240 can comprise a lever that movesaxially. The driver thus can control the change speed mechanism in thecrankcase 174 and vary the transmission operating state among at leastthe parking state, the high speed forward state, the neutral state, thelow speed forward state, and the reverse state by operating the lever244.

[0091] Because of the advantageous configuration of the drive trainrelative to the shift lever unit 240, the shift lever unit 240 ispositioned close proximity to the change speed mechanism of thetransmission 144. The linkage thus can be short enough to make theswitchover mechanism compact and also to improve the feeling that thedriver might have when operating the shift lever unit 240.

[0092] With reference to FIGS. 1-4, the output of the switchovermechanism is transferred to the drive mechanism 146 through the bevelgear 236. In the illustrated arrangement, the bevel gear 236 is coupledwith a forward intermediate shaft 248. The forward drive shaft 150 ispivotally coupled to the forward intermediate shaft 248 through auniversal joint 250. That is, the universal joint 250 comprises a firstyoke 252, a second yoke 254 and a cross pin 256 pivotally coupling thefirst and second yokes 252, 254.

[0093] The forward driveshaft 150 is coupled with a front differentialinput shaft 262 (FIG. 4) of the front differential 124. The frontdifferential housing 122 preferably encloses at least a portion of theinput shaft. The front differential input shaft is coupled with amechanism of the front differential 124, such as a pinion ordifferential gear. A pair of output shafts 262 extends from themechanism of the front differential 124. Each output shaft 262 isconnected to a respective one of the front wheels 56.

[0094] Preferably, the gear case 114 of the rack-and-pinion assembly 112is positioned behind the output shafts 262. This arrangementadvantageously locates the tie-rods and the knuckle arms of the steeringsystem 104 in a space located behind linkages that connect therespective output shafts 263 with the associated front wheels 56. Thus,the knuckle arms can have a sufficient length and bump steering can bereduced. Further, such a placement provides some degree of protection tothese components.

[0095] With reference to FIG. 5, the forward driveshaft 150 extendsforwardly within the tunnel defined by the projection 52 of thefloorboard 50 and generally adjacent to the middle section 202 of theintake duct 186. The forward driveshaft 150 thus is positioned higherthan the horizontal section 51 of the floorboard 50. Accordingly, theforward driveshaft 150 is generally protected from significant impactsfrom rocks, sticks, road debris and the like. In some arrangements, atleast a length of a lower opening of the tunnel can be closed with aprotective plate or the like to further protect both the driveshaft 150and the middle section 202 of the intake duct 186.

[0096] In the illustrated arrangement, a rear intermediate shaft 258also is connected to the bevel gear 236 through a suitable connection.The rear driveshaft 152 is connected to the rear intermediate shaft 258through a spline coupling 260. Other couplings or a unitary shaft canalso be used. The rear driveshaft 152 is coupled with a reardifferential input shaft (not shown) of the rear differential 154. Therear differential input shaft preferably is coupled with the rear wheels58 through another differential mechanism formed within the reardifferential 154.

[0097] The off-road vehicle 30 preferably has other devices, componentsand members. For example, the differentials can be selectively lockablesuch that the differential function can be eliminated on demand.Moreover, a brake system can be provided to slow or stop rotation of thewheels 56, 58 or another driveline component (e.g., the driveshafts). Abrake pedal 270 (FIG. 5) can be disposed next to the accelerator pedal196 and can be connected to brake units that are coupled with the wheels56, 58. In some arrangements, the brake units can comprise disk brakeconfigurations. The driver thus can stop the off-road vehicle 30 byoperating the brake pedal 270.

[0098] Various ducts, conduits, cables and the like other than theforward driveshaft 150 and the air intake duct 186, which aresymbolically indicated by a reference numeral 274 of FIG. 5, also canextend through the tunnel defined by the projection 52 of the floorboard50. For example, a brake cable and a coolant hose can pass therethrough.The brake cable could form a portion of the brake system and connectsthe brake pedal and brake units disposed at the respective wheels 56,58. The coolant hose could extend between the engine 142 and a radiator(not shown) that might be disposed under the hood 134 or in anothersuitable location. Because of this duct and conduit arrangement, thoseducts, conduits and cables also can be placed higher than the horizontalsection 51 of the floorboard 50 and are well protected without impingingupon the driver and passenger seating areas and without substantiallyraising the center of gravity of the vehicle.

[0099] In one arrangement, the crankshaft 176 can be positioned beyondthe imaginary rear vertical plane 86, 86A, 86B and the output shaft 216can be positioned between the forward vertical plane 84 and the rearvertical plane 86, 86A, 86B. In the illustrated arrangement, both theoutput shaft 216 and the crankshaft 176 are disposed between theimaginary forward generally vertical plane 84 and the imaginary reargenerally vertical plane 86. This is also true in the illustratedarrangement even if the imaginary rear vertical plane is defined by theplane 86B. A majority of the illustrated engine unit 148, thus, can belocated generally below the seat unit 66. Such an arrangement allows thewheelbase of the off-road vehicle 30 to be shortened in comparison withan arrangement in which a majority of the engine unit 148 is locatedbehind the seat unit 66. Accordingly, the illustrated off-road vehicle30 benefits from a substantially shortened wheel base which results inimproved maneuverability.

[0100] In the illustrated arrangement, a majority of the engine unit 148also is laterally positioned generally between the seats 68. However, insome arrangement, it may be advantageous to place a majority of theengine unit 148 under one of the seats 68. The illustrated engine unit148 can be accommodated in such a position because the cylinder block158, the cylinder head 160 and the cylinder head cover 170 are inclinedupward. Thus, they can be positioned behind the imaginary rear verticalplane 86, 86A, 86B by slightly shifting the position of the crankshaft176, or the positions of the crankshaft 176 and the output shaft 216,rearward. In some arrangements, the engine 142 can be disposed generallyon its side such that the engine body extends generally horizontallywithout having a significant portion extending upward.

[0101] In the illustrated arrangement, the engine 142 is locatedgenerally rearward of the change speed mechanism including the outputshaft 216. Moreover, the engine is positioned generally rearward of, andlower than, the seating area. Thus, heat generated by the engine 142 canbe substantially isolated from the driver and/or the passenger, andparticularly isolated from the feet of those persons both when seatingand when mounting or dismounting from the vehicle. The seat backs 74further insulate the driver and/or passenger from any heat that mayradiate from the engine or exhaust system. In addition, the cylinderblock 158, the cylinder head 160 and the cylinder head cover 170 in thisarrangement generally are directed rearward and are positioned generallyrearward of the occupants. Thus, it is very unlikely that the engineheat will affect the occupants of the vehicle.

[0102] The exhaust system 168 carries a great deal of heat as well whilethe intake system 164 and the charge former, e.g., the throttle body182, generally do not generate or conduct much heat. The intake system164 and the charge former are generally protected from heat carried bythe exhaust system 168 because the exhaust system 168 is positionedopposite to the intake system 164 in the illustrated arrangement. Thus,the engine heat and the exhaust heat can be generally isolated from theintake system 164 during forward operation of the off-road vehicle 30.The temperature of the intake air, therefore, is not greatly affected bythe heat generated during operation of the off-road vehicle 30 andengine output efficiency can be kept in good condition. Along theselines, placement of a radiator preferably is generally below the airintake such that heat generated in the region of the radiator does notadversely affect engine performance through heating of the air inductedinto the engine.

[0103] Furthermore, in the illustrated intake system 164, the intakesystem 164 generally does not extend along a heat generating orconducting surface of the engine 142. Thus, the engine heat is generallyisolated from the intake system 164 in this arrangement. Also, theillustrated air cleaner 188 is greatly spaced from the engine 142. Assuch, any air that is heated by the engine 142 and the exhaust system168 will not be drawn into the air intake system 164, which improves theengine output efficiency. Additionally, due to the elevated nature ofthe air inlet and air cleaner 188, water also is very unlikely to bedrawn into the intake system 164. Furthermore, because the air cleaner188 is positioned below the hood 134, water is unlikely to splash itsway into the air cleaner.

[0104] As illustrated, the exhaust conduits 208 extend along arelatively lower portion of the off-road vehicle 30 in the illustratedarrangement because the exhaust conduits 208 are directed generallydownward and rearward instead a wrapping around from a forward orlateral surface of the engine. The exhaust conduits 208, thus, aresufficiently spaced apart from the driver and/or the passenger. As aresult, the seats 68 can be positioned closer to the engine 142, whichallows a narrower overall construction for the vehicle or a closermounting of the split seats 68.

[0105] Although the present invention has been described in terms of acertain preferred embodiment, other embodiments apparent to those ofordinary skill in the art also are within the scope of this invention.Thus, various changes and modifications may be made without departingfrom the-spirit and scope of the invention. The scope of the presentinvention is intended to be defined only by the claims that follow.

What is claimed is:
 1. An off-road vehicle comprising a frame, a firstwheel and a second wheel supporting a forward portion of the frame, agenerally vertical longitudinal center plane being defined through saidframe, the first wheel being disposed on one side of the center planeand the second wheel being disposed on an opposite side of the centerplane, a prime mover being supported by the frame, a drive systemconnecting the prime mover to the first and second wheels, a housingenclosing a portion of the drive system,the housing being positionedgenerally on the center plane of the frame, a steering system connectedto the first and second wheels, the steering system comprising asteering control member, the steering control member being adapted foruse by a driver of the vehicle, the steering control member beingoff-set relative to the center plane, an upper end of a steering shaftbeing connected to the steering member, the steering shaft defining anaxis of rotation, the steering shaft being supported by the frame andbeing rotatable about the axis of rotation, a first tie-rod beingconnected to the first wheel and a second tie-rod being connected to thesecond wheel, a coupling assembly joining the steering shaft to thefirst and second tie-rods, the coupling assembly being adapted toconvert rotation of the steering shaft to axial movement of the firstand second tie-rods, a case enclosing at least a portion of the couplingassembly and the case being secured to the housing such that saidcoupling assembly is intersected by the center plane.
 2. The off-roadvehicle as set forth in claim 1, wherein the housing is mounted to theframe.
 3. The off-road vehicle as set forth in claim 2, wherein the caseis secured to the housing by mechanical fasteners.
 4. The off-roadvehicle as set forth in claim 2, wherein the first and second wheels areindependently suspended relative to the frame.
 5. The off-road vehicleas set forth in claim 1, wherein the coupling assembly comprises rodsections that extend outward from the housing, the rod sections beingaxially moveable and each one of the rod sections being adapted forconnection to a corresponding one of the first and second tie-rods. 6.The off-road vehicle as set forth in claim 1, wherein the drive systemcomprises a transmission and a drive mechanism that connects thetransmission to the front and rear wheels, the portion of the drivesystem positioned within the housing including at least a portion of thedrive mechanism.
 7. The off-road vehicle as set forth in claim 1,wherein the portion of the drive system positioned within the housingcontains a differential gear unit that distributes power to the firstand second wheels.
 8. The off-road vehicle as set forth in claim 7,wherein the differential gear unit comprises a pair of output shafts,each of the pair of output shafts being coupled with a corresponding oneof the first and second wheels, the case being positioned longitudinallybehind the output shafts.
 9. The off-road vehicle as set forth in claim1, wherein the housing has a top surface and the case is positioned onthe top surface.
 10. The off-road vehicle as set forth in claim 1,wherein the coupling assembly is a rack-and-pinion assembly.
 11. Theoff-road vehicle as set forth in claim 1, wherein the prime mover is anengine.
 12. An off-road vehicle comprising a frame, a first wheel and asecond wheel being arranged to support a forward portion of the frame, agenerally vertical center plane extending fore and aft along the frame,the center plane generally bisecting the frame, the center plane beinginterposed between the first wheel and the second wheel, a prime moverbeing positioned above a central portion of the frame, a drive systemarranged to transmit power of the prime mover to the first and secondwheels, the drive system comprising a differential gear unit configuredto distribute power to the first and second wheels, a housing having atleast a portion that generally encloses the differential gear unit, thecenter plane intersecting the portion of the housing containing thedifferential gear unit, a steering system connected with the first andsecond wheels, the steering system comprising a steering control member,the steering control member being positioned to a lateral side of thecenter plane, a case enclosing a portion of the steering system and thecase being coupled with the housing and being positioned such that thecenter plane also intersects at least a portion of the case enclosingthe portion of the steering system.
 13. The off-road vehicle as setforth in claim 12, wherein the steering system additionally comprises asteering shaft that is mounted on the frame for rotation, the steeringshaft-defining a rotational axis, a first tie-rod being connected withthe first wheel and a second tie-rod being connected with the secondwheel, a coupling mechanism joining the steering shaft to the tie-rods,the coupling mechanism being adapted to convert rotational movement ofthe steering shaft to axial movement of the first and second tie-rods.14. The off-road vehicle as set forth in claim 13, wherein the couplingmechanism comprises a first and a second rod section extending laterallyoutward relative to the center plane, the first rod section beingconnected to the first tie-rod, the second rod section being connectedto the second tie-rod, the first and second rod sections being axiallymoveable when the steering shaft rotates.
 15. An off-road vehiclecomprising a frame, a first wheel and a second wheel supporting aforward portion of the frame, a generally vertical plane extending foreand aft and being disposed centrally between the first wheel and thesecond wheel, a prime mover being positioned above a portion of theframe, a drive system transmitting power to the first and second wheelsfrom the prime mover, a housing enclosing a portion of the drive system,the housing being intersected by the center plane of the frame, asteering system being connected to the first and second wheels, thesteering system comprising a steering control member that is adapted fordirect control by a driver of the vehicle, the steering control memberbeing positioned substantially to one side of the center plane, a caseenclosing a portion of the steering system that is intersected by thecenter plane, the portion of the steering system that is intersected bythe center plane transforming movement of the steering control memberinto movement of the front wheels, the case being coupled with thehousing that encloses the portion of the drive system.
 16. An off-roadvehicle comprising a frame, a first wheel and a second wheel beingindependently suspended from the frame, the first and second wheel beingsteerable relative to the frame, a prime mover supported by the frame, adrive shaft transferring power from the prime mover, a differential gearunit receiving power from the drive shaft, the differential gear unitsupplying power to the first and second wheels, a generally verticalcenter plane extending in a longitudinal direction and being positionedgenerally equidistant between the first and second wheels, an operatorcontrol member being mounted to the frame assembly and being rotatableabout a first axis, the operator control member being positionedsubstantially on one side of the center plane, a steering mechanismadapted to transform rotation of the control member about the first axisinto generally linear lateral movement of a first rod section and asecond rod section, the first rod section being coupled with a first tierod, the first tie rod being coupled with the first wheel, the secondrod section being coupled with a second tie rod, the second tie rodbeing coupled with the second wheel, the steering mechanism beingpositioned such that it is intersected by the center plane and beingjoined to a casing covering at least a portion of the differential gearunit.
 17. The off-road vehicle of claim 16, wherein the operator controlmember is mounted to an end of a first steering shaft, the firststeering shaft extending generally parallel to the center plane.
 18. Theoff-road vehicle of claim 17, wherein a lower portion of the firststeering shaft is connected to a second steering shaft and the secondsteering shaft comprises an axis of rotation that intersects the centerplane.
 19. The off-road vehicle of claim 16, wherein the steeringmechanism is joined to a top surface of the casing.